1. Field of the Invention
The present invention relates to a non-aqueous electrolyte secondary battery, more specifically, to a constitution of a positive electrode material in a non-aqueous electrolyte secondary battery.
2. Description of the Related Art
Recently, with a view to the worldwide issue of air pollution due to automotive exhaust gas, electric vehicles using electricity as a power source, hybrid vehicles driven by a combination of an engine and a motor, and fuel cell vehicles using a fuel cell as a power source, and the like are attracting attention. Developments of batteries of high energy density and high output density mounted on those vehicles are taking important positions industrially. Further, also regarding vehicles using only an engine as a power source, vehicles carrying a high voltage battery, which enable mounting of various electrically powered equipments, are put into practical use.
Due to its high energy density and discharge voltage, a lithium secondary battery is believed to be a battery suitable for such vehicles, and various developments thereof are progressed.
A lithium secondary battery is comprised of a positive electrode and a negative electrode capable of storing and releasing a lithium ion, and a non-aqueous electrolyte layer. The electrode contains an electrode active material, conductive material, electrolyte, electrolyte salt, binder and the like. The non-aqueous electrolyte layer is composed essentially of an electrolyte salt and a non-aqueous solvent.
When charging and discharging is conducted at high current rate in such a battery, a lithium ion present on an electrolyte inside of an electrode is absorbed rapidly in an electrode active material. By this, the lithium ion concentration in the electrode decreases, lithium ions are diffused and supplied from a non-aqueous electrolyte layer. Lithium ions enter into and exit from a non-aqueous electrolyte layer, and simultaneously electrons from a collector move through a conductive material to cause progress of an electrode reaction, thus performing charging and discharging.
Such an electrode for the lithium secondary battery is produced by mixing an electrode active material, conductive material and binder in a solvent to give a slurry, then, coating the slurry on a collector and drying this (see, Japanese Patent Application Laid-Open No. H7-220722).
An electrode produced by the method of Japanese Patent Application Laid-open No. H7-220722 has a constitution in which an electrode active material and the like are supported by a binder and electrical contact between electrode active materials is maintained by a conductive material.